So.. I made a mistake.... (maybe) and I am hoping to get some help/opinions from you folks

I recently bought a used 870 (for a good deal) locally. It had what appeared to be some surface rust on it (pic of initial rust: http://imgur.com/B6n4x6o), so I took it home and went at it with 0000 steel wool and a copper penny. Long story short... I can't seem to get most of the rust off. I left it to soak in PB Buster for ~24 hours and then went at it with 000 steel wool (NOT 0000 steel wool). Still can't get it out...  Pic of what the current rust looks like (sorry about the 2 different picture angles): Outdoor:
http://imgur.com/CHqPhEz Indoor: http://imgur.com/a/AFDdI

Now, here is where I MAY have made a mistake... The shotgun is now slightly lighter in color on the side that had the rust. Pic for reference: http://imgur.com/qoOryIc (That isn't the sun making that part of the gun shinier). It is moderately noticeable in person (within 15' or so). The gun doesn't really have enough value to warrant a professional cerakote job and my minor OCD/cleaning side needs a solution

Options:

- Let it soak in PB for a few more days and keep grinding away with 000 and 0000 steel wool (not a very good option because the smell makes my apartment REEK - I've also been trying to get this rust off for the better part of 3 days now)

- Spray Paint the receiver/magazine tube (will the rust be able to continue expanding if I degrease and provide several layers of protection over it with krylon/rust-oleum?)

- Leave it as is and oil it every month or so (my OCD will kill me with this option)

TL;DR bought a used 870, thought it had surface rust, can't get all of it out with 000 and 0000 steel wool, PB/WD40 soaking didn't remove much either, thinking about spray canning the receiver/magtube but I am worried about the rust growing/expanding if I rattlecan it.

I can't tell 100% but it looks to me like the rust is gone and the metal is lightly pitted from it. I'd just oil it and scrub that area with an oily rag pretty good and call it done. It looks better than it did. My 870 had rust in about the same area from being carried by the receiver when hunted with by the previous owner. I removed it with steel wool, cleaned it (with hoppes I think?) dried it, then oiled it. I made sure the oil soaked into the small pitted surface where the rust was.

It definitely looks better than it did. This gun was also owned by a hunter before myself. I think that picture may have made it look better than it truly is.. Here is a picture that I just took of the receiver: http://imgur.com/a/AFDdI. I can definitely keep it oiled, but I'm at the point of just using a rust-oleum Rust Converter and then painting over the whole receiver/tube.

Looks fine.

870 expresses are pieces of shit. Deface it at your leisure.

You won't get the pits out of the surface.  The metal is gone.  Have you tried something like a brass brush?  Like a toothbrush but with brass bristles?  It might work some of the rust out of the pits.

Then, try some of the oxpho blue.  I see people recommending that for parkerized surfaces on old M1's and other former military rifles.  

According to the add it will remove the rust in the pits and replace the finish.  I've never used it, but like I said, lots of folks recommend it.

oxpho blue

Well, I respectually disagree about them being pieces of shit, but this makes me feel better about rattle canning it!

Rodger that. I'll pick up a brass bristle brush before I spray paint it!

Don't use a brass brush. While it will likely help scrape off rust, that will deposit brass particles all over it. Then the brass particles don't want to come off, until later, when they leave with your paint.
If you're going to paint it, use a steel wire wheel, and get that thing "in the white" with zero rust left. You'll be able to see any pitting very well when you do that. If the pitting bothers you, fill it in with epoxy. Acetone the whole surface really well, and let it completely dry, before you apply the paint.

Oxpho-blue is crap. All of the liquid "touch up" bluing methods suck, and are expensive. Dicropan is the best one, but that's not saying much. If you're between that and spray paint, I'd go with a rattle can formulated for steel/metal.

You haven't seen as many failures with them as I have. Their QC is horrible and although the finish looks corrosion resistant, it's not.

Wingmasters are a different story.

Looks like blood etching on an Express finish, only bead blasting it will remove it likely. Express guns rust if you look at them funny I would either get it parked or blast it and get some rattlecan Alumihide or Duracote and spray it. My old '67 1100 has blood etching on the receiver from the former owner, I just clean the gun and call it patina.

I bought 2 old  870 wingmasters and 1 of them had some bad pitting and I used some 0000 steel wool and a penny and it took some of it off and then I took some sandpaper and made it smooth but you could still see the pitting. a friend of mine had a sand blaster and he cleaned it up and cant tell where the pitting was. I have some before and after pictures and I can post them later for you. I was watching this youtube video of someone restoring their pitted 870. https://www.youtube.com/watch?v=YBD8g-fNfbU